Slightly before 3.30 British Summer Time (2.30 GMT) on Saturday 21 April 2012, the British Geological Survey recorded an Earthquake 12 km beneath the Welsh seaside resort of Barmouth, on the north side of the Mawddach Estuary. An Earthquake this small and this deep is unlikely to have been noticed by residents of the town, and there is no danger of any damage or casualties.
The location of the 21 April Earthquake. British Geological Survey.
Despite being a long way from any plate margins Wales is still moderately Earthquake prone, suffering a magnitude three quake roughly once every three years, and a magnitude four quake roughly every thirty years. Larger quakes are rarer, but do occur; most recently in 1984 when a quake on the Llŷn Peninsula, Gwynedd, recorded as measuring 5.4 on the Richter Scale, was felt across much of the UK and Ireland, causing damage and minor injuries as far away as Liverpool. The most recent Earthquake related fatality was in Porthmadog in 1940, when an elderly lady fell down a flight of stairs during a quake measuring 4.7 on the Richter Scale. In 1906 Swansea in South Wales was hit by a magnitude 5.2 quake that caused considerable damage. Caernarfon, in Gwynedd, suffered a magnitude 4.9 quake in 1903 and a magnitude 5.0 quake in 1893.
These quakes are the result of a variety of influences; Eurasia is being pushed eastwards by the expansion of the Atlantic Ocean, at the same time Africa is pushing into the continent from the south, which causes a considerable number of quakes in southern and southeastern Europe, and a smaller number in northern Europe. Britain is also subject to stresses caused by expansion of the crust beneath the North Sea, in the Rhine Valley and in the Bay of Biscay, though to a lesser extent. Finally the UK is still undergoing glacial rebound; much of the country was covered by a thick layer of ice until about 10 000 years ago. This pushed down on the rocks beneath it, which are now slowly springing back up again.
The British Geological Survey are interested in hearing from anyone in the area who felt (or didn't feel, which is also data) the quake. This can be reported here.
See also Earthquake in Cumbria, Earthquake in Yorkshire, An Earthquake off the coast of Margate, 8 April 2012, Southwest Poland hit by Earthquake and Earthquakes on Sciency Thoughts YouTube.
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